personally i think 21 miles a week is excessive. 30-40 minutes 4-5 days per week low intensity after weights, or even much shorter high intensity sessions should be fine, for some additional calorie expenditure and conditioning purposes.

personally i think 21 miles a week is excessive. 30-40 minutes 4-5 days per week low intensity after weights, or even much shorter high intensity sessions should be fine, for some additional calorie expenditure and conditioning purposes.